The present invention relates to a membrane filtration device comprising a plurality of planar membrane filter elements which are combined to form a membrane package and which are disposed within the membrane package parallel to and spaced apart from one another, a wall which encloses the membrane package on all sides, and within which at least one inlet chamber which is connected to at least one inlet opening for feeding a fluid to be filtered formed upstream from the membrane filter elements, and at least one outlet chamber which is connected to at least one outlet opening for discharging a filtered fluid portion produced by filtration formed downstream from the membrane filter elements, and an oscillation unit which is connected to the membrane package and the wall to create oscillation in a direction parallel to the membrane filter elements. Another aspect of the present invention relates to a separation method for biologically contaminated wastewater in agriculture.
A core problem in modern agriculture concerns the treatment of contaminated wastewater. As a result of tougher environmental standards, methods which were previously widespread, such as spreading such contaminated wastewater on fields over large areas, can now be considered to only a very limited extent or not at all. Methods are therefore needed for treating such contaminated wastewater efficiently in such a way that it satisfies higher environmental standards and ideally may be disposed of as normal wastewater.
One possible way of achieving this is to treat the wastewater in a sewage treatment plant, for example. However, this involves complex equipment and is therefore both costly and maintenance-intensive. Treatment in a sewage treatment plant is not an economical path, therefore, for treating biological contaminated wastewater produced by agriculture.
A filter technology for treating colloidal suspensions and which can be used on a laboratory scale is basically known for a different technical field from U.S. Pat. No. 4,952,317. The latter relates to a membrane filtration device in which a membrane package composed of a plurality of membrane composites arranged in parallel is made to oscillate, the direction of oscillation being parallel to the surface of the membranes. As a result, a shear force is generated between the membrane surface and the colloidal suspension to be filtered, which prevents clogging of the membrane by solid particles and thus allows filtration to be maintained for a certain duration of operation.
The inventor of the present device and of the present method has realized that this membrane filtration principle is basically suitable as well for filtering biologically contaminated wastewater in agriculture. However, when using the device described in U.S. Pat. No. 4,952,317, problems arose which prohibited any efficient operation for this kind of wastewater. For the device shown therein, various options are described for making the membrane package oscillate. These include reciprocal translational oscillations or circular oscillations which are exerted directly on the membrane package by a drive means. The drive means are either rotary actuators with rigid kinematics, or electromechanical torsional resonators. These are rigidly connected to the membrane package in such a way that any vibration produced inside these vibrating units is meant to be transferred directly to the membrane package. It has been found that efficient membrane filtration of biologically contaminated wastewater in agriculture cannot be achieved in this way, either because the energy input for membrane filtration is too high or because the operating time of the membrane filtration device between the necessary replacement of all the membrane filters is too short.
Another membrane filtration device, comprising a membrane package to which a vibratory motion is imparted by means of a drive mechanism in order to enhance filtration, is known from U.S. Pat. No. 6,322,698 B1. Although a system which is suitable for filtering biologically contaminated wastewater in agriculture, using the approach on which the invention is based, is also described in this prior publication, the publication does not provide any indications as to how this system could be developed in a way that allows membrane filtration of such wastewater to be operated in an economically efficient manner.
A membrane filtration device for separating metals and water by adding precipitators is known from U.S. Pat. No. 7,297,278 B2. However, a disadvantage of this device is the need to add precipitators, which makes it more difficult to conduct the process continuously and which also reduces the economic efficiency of the process due to the required addition of consumables in the form of the precipitators.
The object of the present invention is therefore to provide a device for cleaning biologically contaminated wastewater in agriculture and which can be operated in an economically efficient manner.